1. Field of the Invention
The present invention relates to an aspect ratio converting apparatus provided in a TV picture display unit and, more particularly, to an aspect ratio converting apparatus adopting a side panel system.
2. Description of the Related Art
In the NTSC system, the aspect ratio of a TV picture is 4:3. However, high definition television (HDTV) has recently been being put to practical use. In HDTV, a wide aspect ratio, namely, an aspect ratio of 16:9 is adopted. In order to display a picture having an aspect ratio of 4:3 in HDTV, it is necessary to convert the aspect ratio from 4:3 to 16:9.
However, if the the aspect ratio is converted at different compression ratios in the horizontal direction and in the vertical direction, the picture is distorted. It is therefore necessary to convert the aspect ratio at the same compression ratio in the horizontal direction and in the vertical direction. For example, when there is a "round" pattern in the picture before conversion, the "roundness" must be maintained after conversion. This condition is sometimes called "maintenance of roundness".
FIG. 1 shows a picture 6 having an aspect ratio of 4:3 and a picture 8 having an aspect ratio of 16:9.
In the picture 6, a picture region 10 (surrounded by the broken lines) is a region in which picture information can exist as video signals. A display region 12 (surrounded by the solid lines) is a region in which a picture is actually displayed on a TV picture display unit, and an overscanning region 14 is a region in which a picture is not displayed on the display unit. In the display unit, the ratio of the horizontal width and the vertical width of the display region 12 is ordinarily set to be 4:3 as the picture region 10.
In the picture 8 having a wide aspect ratio, the reference numeral 20 represents an overscanning region. Among the picture information in a picture region 16, only the picture information in a display region 18 is actually displayed.
As a system for converting the picture 6 having an aspect ratio of 4:3 into the picture 8 having an aspect ratio of 16:9, a "side panel system" is conventionally known.
In this system, as shown in FIG. 1, the picture region 10 is first compressed equally both in the horizontal direction (H) and the vertical direction (V), as shown in FIG. 1. In this case, in the conventionally known "cut mode" in the side panel system, both ends of the picture region 10 in the horizontal direction are first cut by a predetermined width d, and the picture information in the remaining region (period) 100 is compressed.
It is because there are a few TV signals with a part of the picture information missing at both side ends of a picture at the start and end (right and left ends in the picture region 10) of one horizontal scanning period 104 that both ends of the picture region 10 are cut at the predetermined width d.
By the above-described compression of the picture, the picture information in a partial region 102 of the wide picture region 16 is obtained. However, there is no picture information in both side regions S1 of the region 102.
As a countermeasure, a side panel image having a predetermined luminance (generally gray or black) is inserted into the regions S1, thereby constituting a picture having an overall aspect ratio of 16:9.
FIG. 2 shows an example of a display in the cut mode in the side panel system. On both sides of a compressed picture 21, a side panel image 22 having a predetermined luminance is displayed.
In FIG. 1, the ratio of the horizontal width and the vertical width of the compressed picture in the horizontal direction in the actual displaying region (the overlapping portion of the region 18 and the region 102) is set to be 4:3 in most cases in the same way as the aspect ratio of the picture 6. In order to realize the ratio of 4:3 the cut width d is determined in correspondence with the amount of overscanning in the vertical direction.
FIG. 3 shows a conventional aspect ratio converting apparatus.
In FIG. 3, a video signal 200 and a horizontal synchronization signal 202 are input to an aspect ratio converting portion 30. The aspect ratio converting portion 30 inputs a picture having an aspect ratio of 4:3 and outputs a picture having an aspect ratio of 16:9 by compressing the picture and adding side panel images thereto.
A setting portion 32 is composed of a ROM, etc., and stores the set value of the horizontal width of the region 100 (see FIG. 1). A controller 34 composed of a microcomputer, etc. reads the set value from the setting portion 32 and controls the aspect ratio converting portion 30.
If a TV signal is a luminance and color difference system, two systems of aspect ratio apparatuses are necessary, and if a TV signal is an RGB system, three systems thereof are necessary.
The above-described side panel system, however, suffers from the following problems. In the above-described cut mode, the horizontal width of the side panel image is enlarged, as shown in FIG. 2. Although there are actually many TV signals for picture information in the region having the predetermined width d shown in FIG. 1, both ends of the picture are uniformly cut in the cut mode and the width of the side panel image is therefore enlarged by the width corresponding to the cut width. In addition, the important picture information existing in the cut region is discarded.
To eliminate this problem, the present inventors have devised a "wide mode". This is a method of displaying all the picture information in the horizontal scanning period 104 without cutting the ends of the picture region 10. By adopting this mode, it is possible to reduce the horizontal width of the side panel image.
In the wide mode, however, if there is no picture information at the side ends of the picture, the following problem occurs.
FIG. 4 shows an example of a display in the wide mode. In the wide mode, a side panel image 22 having a smaller width is inserted into a region S2. If there is no picture information at the side ends of the picture region 10, an offensive black line 24 indicating that there is no data is displayed on the boundary between the compressed picture 21 and the gray side panel image 22.
Conventional aspect ratio converting apparatus of the side panel system are disclosed, for example, in Japanese Patent Laid-Open Nos. Hei 2-152380 and Hei 2-92077. In these apparatuses, the aspect ratio is converted without distorting the picture by adding a side panel image to the vacant picture region.
In neither of these apparatuses, however, is the case in which there is no information at the side ends of a picture or the case in which there is picture information at the side ends of a picture taken into consideration. Therefore, these apparatuses suffer from either of the above-described problems.
Another example of a conventional aspect ratio converting apparatus is that disclosed in Japanese Patent Laid-Open No. Hei 2-107080. This apparatus allows a converting mode to be selected from a plurality of modes. When a first mode is selected (see FIG. 2(a) in the specification), the aspect ratio is converted with some distortion in the picture. When a second mode is selected (FIG. 2(b) in the specification), the aspect ratio is converted by the conventional side panel system. When a third mode is selected (FIG. 2(c) in the specification), the aspect ratio is converted with the upper and lower portions of the original picture partially cut.
In this apparatus, however, neither the case in which there is no information at the side ends of a picture not the case in which there is picture information at the side ends of a picture is not taken into consideration.